thermal conductivity enhancement in nanofluids

154 Pages·2014·1.42 MB·English

by  Anand Natchimuthu Chinnaraj

Southern Illinois University Carbondale
OpenSIUC
Theses Theses and Dissertations
12-1-2011
THERMAL CONDUCTIVITY
ENHANCEMENT IN NANOFLUIDS -
MATHEMATICAL MODEL
Anand Natchimuthu Chinnaraj
Southern Illinois University Carbondale, [email protected]
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Natchimuthu Chinnaraj, Anand, "THERMAL CONDUCTIVITY ENHANCEMENT IN NANOFLUIDS -MATHEMATICAL
MODEL" (2011).Theses.Paper 758.
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THERMAL CONDUCTIVITY ENHANCEMENT IN NANOFLUIDS
-MATHEMATICAL MODEL

By
Anand Natchimuthu Chinnaraj
B.TECH, Bharathiyar University, Coimbatore 2004

A Thesis
Submitted in Partial Fulfillment of the Requirements for the
Masters of Science Degree

Department of Mechanical Engineering and Energy Process
In the Graduate School
Southern Illinois University Carbondale
December 2011
THESIS APPROVAL

THERMAL CONDUCTIVITY ENHANCEMENT IN NANOFLUIDS
-MATHEMATICAL MODEL

By
Anand Natchimuthu Chinnaraj

A Thesis Submitted in Partial
Fulfillments of the Requirements
For the Degree of
Master of Science
In the field of Mechanical Engineering

Approved by
Dr. Kanchan Mondal, Chair
Dr. Tsuchin P Chu
Dr. James A Mathias

Graduate School
Southern Illinois University
November 07, 2011
AN ABSTRACT OF THE THESIS OF
ANAND NATCHIMUTHU CHINNARAJ, for the Masters of Science degree in Mechanical
Engineering and Energy Processes presented on 07, November, 2011, at Southern Illinois
University, Carbondale.
TITLE: THERMAL CONDUCTIVITY ENHANCEMENT IN NANOFLUIDS
-MATHEMATICAL MODEL
MAJOR PROFESSOR: Dr. Kanchan Mondal
A mathematical model for thermal conductivity enhancement in nanofluids was developed
incorporating the following: formation of nanoparticles into nanoclusters, nanolayer fluid
thickness, Brownian motion and volume fraction of nanoclusters. The expression developed was
successfully validated against experimental data obtained from the literature. The model was
able to comprehensively explain the enhanced thermal conductivity of nanofluids. Following the
validation, parametric study resulted in drawing up some important conclusions. It was found
that in this study that the nanoparticles tend to form nanoclusters and the volume fraction of the
nanoclusters and the trapped fluid in the nanocluster contributed to the overall thermal
conductivity. Various types of cluster formation were analyzed and it was generally found that
employing spherical nanocluster models were more effective in predicting the thermal
conductivity of nanofluids. The contribution of Brownian motion of nanoparticles to the overall
thermal conductivity of nanofluids was found to be very important albeit small in comparison to
the cluster effect. The study investigated the impact of the nanoparticle size which has been
suggested to be an important factor the results were found to be in concord with the
experimental observations. The values of the thermal conductivity for different nanofluid
combinations were calculated using the expression developed in this study and they agreed with
i
published experimental data. The present model was tested against several nanofluid
combinations. The variables scrutinized under the parametric study to understand thermal
conductivity enhancement were nanoparticle diameter, nanolayer thickness, nanocluster stacking
and Brownian motion. From the study, it was observed that Brownian motion is significant only
when the particle diameter is less than 10 nm. The major factor for the thermal conductivity
enhancement in nanofluids is the formations of nanoclusters and the thickness of the nanolayer.
The combination of the base fluid and nanoparticles to from nanoclusters is expected provide
better cooling solution than the conventional cooling fluids.

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ACKNOWLEDGEMENTS

It has been a wonderful experience working with the Department of Mechanical Engineering and
Energy Processes during my studies at Southern Illinois University at Carbondale. I would like
to thank the following for their assistance and advice throughout the duration of my thesis.
Firstly, I thank my advisor Dr. Kanchan Mondal for giving me this opportunity to work under
him. His helpful advice, support and understanding are exceptional. Without his guidance and
persistent help this thesis would not have been possible.
I also thank the members of committee Dr. Tsuchin.P.Chu and Dr. James.A.Mathias for their
time and effort.
I am extending my special thanks to Department of Mechanical Engineering and Energy
Processes. I am very much grateful to department chair Dr. Rasit Koc who accepted me in this
program and for the financial support and guidance throughout my study here at Southern Illinois
University. My regards to Debbie Jank and Toni Baker for extending their helpful hand.
I appreciate the help that I got from my friends Vijay, Saravanan, Sasisekaran, Justin, Eric and
others.
I also thank all the professors whom I met during the last two years at Southern Illinois
University, Carbondale.
I would like to thank my family for their love, long-standing support that they have given me
during my studies here in United States of America.

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TABLE OF CONTENTS

ABSTRACT………………………………………………………………………………………i
ACKNOWLEDGEMENTS ........................................................................................................... iii
TABLE OF CONTENTS …………………………………………………………… iv
LIST OF TABLES ......................................................................................................................... vi
LIST OF FIGURES ...................................................................................................................... xii
NOMENCLATURE ................................................................................................................... xvii
CHAPTER 1 INTRODUCTION ................................................................................................. 1
CHAPTER 2 REVIEW OF LITERATURE ................................................................................. 5
A.Overview ..................................................................................................................................... 5
B. Mathematical Models for thermal conductivity of nanofluids ................................................... 5
C. Experimental and Modeling work on thermal conductivity of nanofluids ................................ 9
D. Conclusion ............................................................................................................................... 12
CHAPTER 3 DEVELOPMENT OF MATHEMATICAL MODEL ........................................ 13
CHAPTER 4 DISCUSSION OF RESULTS & COMPARISION WITH OTHER MODELS . 25
CuO – Water: 18 nm .................................................................................................................... 29
CuO – Water: 23.6 nm ................................................................................................................. 32
CuO-EG 30.8 nm .......................................................................................................................... 35
A O – Water 60.4 nm ................................................................................................................ 38
A O – EG 26 nm ...................................................................................................................... 40
iv
T O - Water 10 nm ..................................................................................................................... 42
T O - Water 34 nm ..................................................................................................................... 44
T O - Water 27 nm ..................................................................................................................... 46
T O - EG 34 nm ......................................................................................................................... 49
ZnO – Water 10 nm ...................................................................................................................... 51
ZnO – Water 30 nm ...................................................................................................................... 53
ZnO – EG 60 nm ........................................................................................................................... 55
Cu-Water 100 nm .......................................................................................................................... 57
Al-Water 20 nm ............................................................................................................................ 59
Fe-EG 10nm .................................................................................................................................. 61
Conclusion .................................................................................................................................... 64
CHAPTER 5 PARAMETRIC STUDY OF THE PROPERTIES OF NANOFLUIDS ............. 65
A.Effect of Nanolayer thickness on the overall thermal conductivity of nanofluids: .................. 65
B.Effect of particle diameter on effective thermal conductivity of nanofluids ............................ 83
C.Effect of Brownian motion on thermal conductivity of nanofluids .......................................... 96
E.Discussion of results of the parametric studies ....................................................................... 120
CHAPTER 6 CONCLUSION ................................................................................................ 122
APPENDICES ............................................................................................................................ 130
VITA 131

v
LIST OF TABLES

Table 4. 1.Volume fraction and mean diameter of cluster for CuO (18 nm) – ............................. 31
Table 4. 2. Comparison of k values for CuO (18 nm) – Water nanofluids. ............................... 31
eff
Table 4. 3.Volume fraction and mean diameter of cluster for CuO (23.6 nm) – water nanofluids
....................................................................................................................................................... 33
Table 4. 4.Comparison of k values for CuO (23.6 nm) – Water nanofluids .............................. 34
eff
Table 4. 5. Volume fraction and mean diameter of cluster for CuO (30.8 nm) – EG nanofluids.
....................................................................................................................................................... 36
Table 4. 6.Comparison of k values for CuO (30.8 nm) – EG nanofluids. ................................. 37
eff
Table 4. 7. Volume fraction and mean diameter of cluster for Al O (60.4 nm) – Water
2 3
nanofluids. ..................................................................................................................................... 38
Table 4. 8 Comparison of Effective Thermal Conductivity values for Al O (60.4 nm) Water
2 3
nanofluids. ..................................................................................................................................... 39
Table 4. 9. Volume fraction and mean diameter of cluster for Al O (26 nm) – EG nanofluids. 40
2 3
Table 4. 10.Comparison of Effective Thermal Conductivity values for Al O (26 nm)– EG
2 3
nanofluids. ..................................................................................................................................... 41
Table 4. 11 Volume fraction and mean diameter of cluster for TiO (10 nm ) – Water nanofluids
2
....................................................................................................................................................... 43
Table 4. 12.Comparison of k values for TiO (10 nm) – Water nanofluids .............................. 43
eff 2
Table 4. 13 Volume fraction and mean diameter of cluster for TiO (34 nm)– Water nanofluids 45
2
Table 4. 14 Comparison of Effective Thermal Conductivity values TiO (34 nm) – Water
2
nanofluids ...................................................................................................................................... 45
Table 4. 15 Volume fraction and mean diameter of cluster for TiO (27 nm) – water nanofluids47
2
vi
Table 4. 16 Comparison of Effective Thermal Conductivity values for TiO (27 nm) – water
2
nanofluids ...................................................................................................................................... 48
Table 4. 17 Volume fraction and mean diameter of cluster for TiO (34 nm) - EG 34 nanofluids
2
....................................................................................................................................................... 49
Table 4. 18 Comparison of Effective Thermal Conductivity values for TiO2 (34 nm) - EG 34
nanofluids ...................................................................................................................................... 50
Table 4. 19 Volume fraction and mean diameter of cluster for ZnO (10 nm) -Water nanofluids 51
Table 4. 20 Comparison of Effective Thermal Conductivity values for ZnO (10 nm) -Water
nanofluids ...................................................................................................................................... 52
Table 4. 21 Volume fraction and mean diameter of cluster for ZnO (30 nm) – Water nanofluids
....................................................................................................................................................... 53
Table 4. 22 Comparison of Effective Thermal Conductivity values for ZnO (30 nm) – Water
nanofluids ...................................................................................................................................... 54
Table 4. 23 Volume fraction and mean diameter of cluster for ZnO (60 nm) – EG ..................... 55
Table 4. 24 Comparison of Effective Thermal Conductivity values for ZnO (60 nm) – EG
nanofluids ...................................................................................................................................... 56
Table 4. 25 Volume fraction and mean diameter of cluster for Cu (100 nm) – Water nanofluids 57
Table 4. 26 Comparison of Effective Thermal Conductivity values for Cu (100 nm) – Water
nanofluids ...................................................................................................................................... 58
Table 4. 27 Volume fraction and mean diameter of cluster for Al (20 nm) – Water ................... 59
Table 4. 28 Comparison of Effective Thermal Conductivity values for Al (20 nm) – Water
nanofluids ...................................................................................................................................... 60
Table 4. 29 Volume fraction and mean diameter of cluster for Fe (10 nm) – Water nanofluids .. 62
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